Composite wood products, such as oriented strand board (OSB), oriented strand lumber (OSL), or laminated strand lumber (LSL), among others, are formed using wood strands that are bonded together. FIG. 1 illustrates generally an example of a composite wood product comprised of rectangular wood strands. In some composite wood products, the strands are commonly aligned, such as in the direction indicated by the arrow 101. The wood strands used in some composite wood products are rectangular, and can be substantially uniform in length, width, and thickness. FIG. 2 illustrates generally an example of a wood strand 102 that has a particular length (L), width (W), and thickness (T).
The composite wood product forming process generally involves stranding or flaking a log into wood strands of a particular size or shape, treating the wood strands (e.g., drying the strands or mixing the strands with an adhesive or resin), aligning or otherwise distributing the wood strands to form a layered mat of strands, and pressing the mat under heat and pressure, in the presence of moisture, for a particular period of time.
Many variables contribute to differences among composite, strand-based wood products. Some variables include the type of wood used for the strands, the size or shape of the strands, the uniformity or density of the composite products, or the bonding process used to form the composite products.
Some composite, strand-based wood products are defined by ASTM International standards. For example, under ASTM D5456-11a, LSL is comprised of wood strands having a least dimension of 0.10 inches (2.54 mm) or less, and an average length that is a minimum of 150 times that least dimension. Under ASTM D5456-11a, OSL is comprised of wood strands having a least dimension of 0.10 inches (2.54 mm) or less, and an average length that is a minimum of 75 times that least dimension. In other words, LSL is generally comprised of strands having a length-to-thickness ratio of about 150:1, and OSL is generally comprised of strands having a length-to-thickness ratio of about 75:1. LSL and OSL can be used for applications such as studs or millwork components, among others.
The properties of a formed, strand-based wood product can depend on the above-mentioned variables, among others. For example, a formed product's modulus of elasticity (a measure of material stiffness or rigidity) or modulus of rupture (a measure of bending a material can withstand without breaking) can be a function of strand length and stand alignment, among other variables. In some products, a higher modulus of elasticity can correspond to longer strands that are better aligned than in a product using similar length strands that are more poorly or irregularly aligned.
Various systems can be used to orient wood strands. These systems are generally optimized to align strands in a common direction, to uniformly distribute strands across a mat area of the system, and to operate at an economical throughput.
Some orienter systems use rotating disks, mounted on multiple shafts, disposed under a supply of wood strands. Strands fall from the supply onto the disks while the disks are rotating, and the strands become aligned as they descend between the disks. The aligned strands form a mat below the disks, such as on a moving conveyor. Barnes, in U.S. Pat. No. 5,487,460, entitled “Short Strand Orienter,” describes an orienter with multiple decks of rotating disks, and the multiple decks have different inter-disk spacings. For example, an inter-disk spacing on an upper deck of disks can be wider than an inter-disk spacing on a lower deck of disks. Similarly, Knudson, in U.S. Pat. No. 6,752,256, entitled “System for Improving Wood Strand Orientation in a Wood Strand Orienter using Rotating Orienting Fingers,” describes an orienter with “pre-orienting” shafts positioned above orienter discs.
Other orienter systems use vanes, or parallel plates, disposed under a supply of wood strands. Strands fall from the supply onto the plates and become aligned as they descend between the plates. Etzold, in U.S. Pat. No. 4,058,201, entitled “Method and Apparatus for Orienting Wood Strands into Parallelism,” describes adjacent plates that reciprocate in opposite directions relative to each other to encourage strands into a common orientation.
Barnes et al., in U.S. Pat. No. 5,676,236, entitled “Vane Orienter with Wipers,” describes partition walls that define passages, and wipers disposed in the passages to wipe strands that may otherwise plug the orienter.